8

This is to do with the following code, which uses a for loop to generate a series of random offsets for use elsewhere in the program.

The index of this for loop is unused, and this is resulting in the 'offending' code being highlighted as a warning by Eclipse / PyDev

def RandomSample(count):    
    pattern = []
    for i in range(count):
        pattern.append( (random() - 0.5, random() - 0.5) )

    return pattern

So I either need a better way to write this loop that doesn't need a loop index, or a way to tell PyDev to ignore this particular instance of an unused variable.

Does anyone have any suggestions?

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1

7 Answers 7

Reset to default
18

Just for reference for ignoring variables in PyDev

By default pydev will ignore following variables 

['_', 'empty', 'unused', 'dummy']

You can add more by passing supression parameters

-E, --unusednames  ignore unused locals/arguments if name is one of these values

Ref: http://eclipse-pydev.sourcearchive.com/documentation/1.0.3/PyCheckerLauncher_8java-source.html

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2 Comments

PyDev suppresses warnings for unused variables if they start with an underscore. So _i would also work.
You could also add "i=i". This has the advantage that is would work in any development environment regardless of what builtin variable ignores it has.
5

How about itertools.repeat:

import itertools
count = 5
def make_pat():
    return (random() - 0.5, random() - 0.5)
list(x() for x in itertools.repeat(make_pat, count))

Sample output:

[(-0.056940506273799985, 0.27886450895662607), 
(-0.48772848046066863, 0.24359038079935535), 
(0.1523758626306998, 0.34423337290256517), 
(-0.018504578280469697, 0.33002406492294756), 
(0.052096928160727196, -0.49089780124549254)]
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1 Comment

As a function: fn = lambda count: itertools.repeat(lambda: (random() - 0.5, random() - 0.5), count)
4 
randomSample = [(random() - 0.5, random() - 0.5) for _ in range(count)]

Sample output, for count=10 and assuming that you mean the Standard Library random() function:

[(-0.07, -0.40), (0.39, 0.18), (0.13, 0.29), (-0.11, -0.15),\
(-0.49, 0.42), (-0.20, 0.21), (-0.44, 0.36), (0.22, -0.08),\
(0.21, 0.31), (0.33, 0.02)]

If you really need to make it a function, then you can abbreviate by using a lambda:

f = lambda count: [(random() - 0.5, random() - 0.5) for _ in range(count)]

This way you can call it like:

>>> f(1)
f(1)
[(0.03, -0.09)]
>>> f(2)
f(2)
[(-0.13, 0.38), (0.10, -0.04)]
>>> f(5)
f(5)
[(-0.38, -0.14), (0.31, -0.16), (-0.34, -0.46), (-0.45, 0.28), (-0.01, -0.18)]
>>> f(10)
f(10)
[(0.01, -0.24), (0.39, -0.11), (-0.06, 0.09), (0.42, -0.26), (0.24, -0.44) , (-0.29, -0.30), (-0.27, 0.45), (0.10, -0.41), (0.36, -0.07), (0.00, -0.42)]
>>>

you get the idea...

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9 Comments

This just renamed the unused variable to _ and so isn't really any better, unless Eclipse ignores that specially.
Does PyDev not give the same warning about _ being unused?
'_' is a dummy variable, Eclipse should not complain, but I don't know, as I have never developed Python on that platform. Good luck, and please let me know if it does complain.
Nope, _ doesn't get the warning.
'_' isn't special in any way. Really, Eclipse should complain if it does in other cases. Of course, in this case, I feel just ignoring eclipse's complaint is valid.
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2

Late to the party, but here's a potential idea:

def RandomSample(count):
    f = lambda: random() - 0.5
    r = range if count < 100 else xrange # or some other number
    return [(f(), f()) for _ in r(count)]

Strictly speaking, this is more or less the same as the other answers, but it does two things that look kind of nice to me.

First, it removes that duplicate code you have from writing random() - 0.5 twice by putting that into a lambda.

Second, for a certain size range, it chooses to use xrange() instead of range() so as not to unnecessarily generate a giant list of numbers you're going to throw away. You may want to adjust the exact number, because I haven't played with it at all, I just thought it might be a potential efficiency concern.

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2 Comments

Why not just always use xrange?
That's a good alternative. I'm making the assumption that creating a generator for only two iterations might be more expensive than creating a list of only two elements. I, of course, have no benchmarks on how expensive generators and lists may or may not be, but somehow I have a feeling that if xrange(2) is more efficient than range(2) then something is terribly wrong with the implementation.
1

There should be a way to suppress code analysis errors in PyDev, like this:

http://pydev.org/manual_adv_assistants.html

Also, PyDev will ignore unused variables that begin with an underscore, as shown here:

http://pydev.org/manual_adv_code_analysis.html

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0

Try this:

while count > 0:
    pattern.append((random() - 0.5, random() - 0.5))
    count -= 1
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0 
import itertools, random   

def RandomSample2D(npoints, get_random=lambda: random.uniform(-.5, .5)):
    return ((r(), r()) for r in itertools.repeat(get_random, npoints))
  • uses random.uniform() explicitly
  • returns an iterator instead of list
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